Sentinel lymph node mapping in the management of colorectal cancer: preliminary report

The problem of understaging the lymph node status in colorectal cancer because of missed micrometastases led authors to investigate the role of sentinel node (SN) mapping also in colorectal malignancies. The aim of this study was to evaluate the feasibility of the technique and to correlate the results with some characteristics of the primary tumor.

Sentinel lymph node mapping was performed in 23 patients who underwent a standard lymphadenectomy for colorectal cancer. The vital dye Patent Blue had been injected into the peritumoral subserosa in vivo in 17 cases and ex vivo in seven, including one case where the in vivo method did not allow to identify the sentinel node. The nodes that took up the dye were removed and analyzed with standard hematoxylineosin staining in serial sections. Immunohistochemistry (AE1-AE3 cytokeratin markers) was performed in hematoxylineosin-negative nodes. SN status was related to the status of the other lymph nodes in the surgical specimen analyzed with the standard technique and to the following characteristics of the primary tumor: stage, grade and diameter.

The in vivo technique allowed to identify the SN in 16/17 cases (94.1%), the ex vivo technique in 7/7. A total of 336 lymph nodes dissected from the surgical specimens was analyzed, with an average of 14.6 nodes per patient (range, 7-35). Of these nodes 58 were SNs, with an average of 2.5 nodes per patient (range, 1-8). In the 19 cases where the SN was tumor negative, the non-SNs were also negative (specificity: 100%), whereas in the four cases where the non-SNs were positive, in two cases the SN was positive and in two cases of pT3 rectal carcinoma the SN was negative (sensitivity: 50%). Immunohistochemistry did not modify the negative results of the standard hematoxylin-eosin evaluation.

The method used to identify the SN using vital dye proved to be easy to use both in vivo and ex vivo and allowed to identify the SN in all cases. The preliminary results indicate that there is a risk of false negative findings and therefore further studies are required to improve the sensitivity and the specificity of the technique and to evaluate the role of SN mapping in colorectal cancer management.